hm, from what I’ve been taking from the sequence quantum physics seems to apply fully at all levels, and the idea of it working differently/not applying is simply a matter of scale. For example an event causing a “split” affecting significantly macro objects almost entirely decohere, but not perfectly avoiding any kind of hard cutoff. Large systems definitely appear to work differently when you look at them on a large scale, but.. that appearance or classical hallucination is just an emergent property of underlying quantum effects.
Saying the quantum mechanics itself breaks down.. does not fit with the mental picture of reality I’ve taken from this, reality as entirely locally computable and with higher level effects based entirely on the base level substrate behavior. I’d like you to clarify what you mean by “break down”, and preferably how reality would choose where to draw any line between scales where quantum mechanics does and does not break down?
I have read quantum physics has issues with gravity, perhaps that is what you’re referring to? If so, I’d be interested in recommended further reading.
To chime in as a person with grad-level training in the subject matter: there is a glaring tension between Quantum Field Theory and General Relativity in the low-energy macroscopic-size limit, which is very bad. How bad? Imagine “proving” that 1=2 in Peano arithmetic, something like that. The issue is the black hole: firewall or horizon? question. GR says that there is nothing locally special about crossing the event horizon (and must be applicable, since GR has been tested in this low-curvature regime), while QFT says that, after a while, the horizon becomes a high-energy incinerator (and must be applicable, since quantum entanglement has been tested in this low-energy regime). The best physics minds on the planet are at a loss to explain the problem. Last time something like that happened in physics, a completely new and unexpected theory eventually resulted. Odds are, we are in for a similar paradigm shift some day, hopefully soon.
from what I’ve been taking from the sequence quantum physics seems to apply fully at all levels, and the idea of it working differently/not applying is simply a matter of scale.
Nobody’s resolved the fundamental problems between QM and general relativity (GR). EY comes close to claiming that MWI will do the trick, but it hasn’t yet. At one point he even says that (paraphrasing) reality is a dream, and the dream satisfies special relativity—at which point one has to ask why the dream doesn’t satisfy general relativity.
Large systems definitely appear to work differently when you look at them on a large scale, but.. that appearance or classical hallucination is just an emergent property of underlying quantum effects.
See the previous note. Emergence is just another word for “magic.”
Saying the quantum mechanics itself breaks down.. does not fit with the mental picture of reality I’ve taken from this, reality as entirely locally computable
This is an unfortunate side-effect of EY’s tone in the QM sequence.
I’d like you to clarify what you mean by “break down”, and preferably how reality would choose where to draw any line between scales where quantum mechanics does and does not break down?
The most evident problem in accepting both QM and SR simultaneously is that they substantially disagree on the value of the vacuum energy density.
What I think you’re saying, correct me if I’m wrong, is that there’s a few big unknowns as to how QM applies to gravity or on cosmological scales, and because of this the answer to my chain of reasoning is “we just don’t know”? That there’s major unknowns is entirely reasonable/accurate, but.. I’m struggling to see exactly how the very real and important unknowns apply specifically to my reasoning.
Simply put: Where, in the line of reasoning, do you think the unknown of quantum gravity trips up the logic, and why?
It’s seems quite possible that in discovering the answers behind the big unknowns we’ll change some underlying assumptions and render my reasoning unworkable. But I don’t see where in the line of reasoning not knowing vacuum energy density, or quantum gravity, causes a problem. And given that, it seems like working with the best available theory means applying certain aspects of QM at universal scale is not unreasonable, though we should expect we may need to update models once some big unknowns are resolved.
I think my use of emergence does not fall into the emergence/magic trap, since I am not attempting to explain anything about how large scale systems behave through emergence, my statement is purely that whatever the details of how macro systems work the large scale effects are caused by local physics being consistently applied and only appearing to work differently due to taking a larger view. Even though I used the word “emergence”, my sentence can be reworded with my intended meaning if you swap it to “emerges from”, which is specifically allowed by that post.
Also, you think my picture of reality as locally computable is “an unfortunate side-effect of EY’s tone in the QM sequence”? If that’s the case, do you dispute reality as locally computable? I’d be interested in sources which coherently argue for reality being non-locally computable.
What I think you’re saying, correct me if I’m wrong, is that there’s a few big unknowns as to how QM applies to gravity or on cosmological scales, and because of this the answer to my chain of reasoning is “we just don’t know”?
We do know—QM predicts the wrong vacuum energy density by several orders of magnitude. We’ve measured this value empirically. Read the Baez link; he explains everything pretty clearly.
my sentence can be reworded with my intended meaning if you swap it to “emerges from”, which is specifically allowed by that post.
The critical unanswered question is how “underlying quantum effects” generate the (observed) geometry of space-time. If there were a solution to that question, I’d take no issue with you saying it emerges from those quantum effects—but we don’t know if it’s actually the other way around, that is, if it’s actually relativistic effects on the microscale that generate quantum phenomena. Or if this is just the wrong question entirely, and that both are caused by a third thing.
That’s how you fell into the emergence/magic trap.
EY has to spend a lot of time in the QM sequence insisting that QM is natural and fundamental to get over people’s preconceptions of it as unnatural. However, that leads to people taking it as the unique baseline physical theory, which it is not.
Okay, I think I see where you’re coming from better now. I have read that link, and at least feel like I conceptually understand some of the problems with applying quantum physics to the large scale. However, I’m still very curious as to exactly how the incompatibility in theories applies to this specific argument, and curious as to whether looking at a purely quantum universe (making the assumption that there is some way to derive relativistic experimental results from QM that we’ve missed, rather than that QM needs major changes) would give the results I’m describing, or whether I’m misunderstanding something about amplitude or thermodynamics in a heat death.
Hm, how to explain clearly.. It seems like what’s being said is QM is at odds with observation (vacuum energy density) and at odds with our other best theory, relativity, (event horizon, thanks for chiming in shminux), so QM is wrong or incomplete in some way. I accept this as a likely conclusion, though I do not understand either theory deeply enough to be able to follow the arguments for inconsistency in full.
However, dismissing a thought experiment about a widely used theory with some possible implications (if I’ve not missed anything and have understood various things better than I’d guess I have, that chain of reasoning could show a certain interpretation (MW) is incompatible with finite space+infinite time, while a different interpretation (collapse) would not be), due to the underlying theory (QM) being wrong/incomplete for other reasons seems.. limiting. Even if the line of reasoning only holds meaning with the assumption that the universe is fundamentally quantum, local, and macro effects are all explainable in principle by the laws which govern the smallest parts, I’m interested in whether or not it holds.
I’m primarily trying to refine my mental model of how decoherence works with these thoughts, and an answer focused on whether in a quantum universe would, from our current understanding of quantum physics, do as I suppose (that is, in finite space+infinite time, it could never even slightly decohere due to probability 1 arriving at an identical configuration eventually), or have I made some error in my reasoning which can be explained and would allow me to improve my model of decoherence?
From a quick glance at your argument, it seems to me that quantum mechanics breaks down on the cosmological scale.
hm, from what I’ve been taking from the sequence quantum physics seems to apply fully at all levels, and the idea of it working differently/not applying is simply a matter of scale. For example an event causing a “split” affecting significantly macro objects almost entirely decohere, but not perfectly avoiding any kind of hard cutoff. Large systems definitely appear to work differently when you look at them on a large scale, but.. that appearance or classical hallucination is just an emergent property of underlying quantum effects.
Saying the quantum mechanics itself breaks down.. does not fit with the mental picture of reality I’ve taken from this, reality as entirely locally computable and with higher level effects based entirely on the base level substrate behavior. I’d like you to clarify what you mean by “break down”, and preferably how reality would choose where to draw any line between scales where quantum mechanics does and does not break down?
I have read quantum physics has issues with gravity, perhaps that is what you’re referring to? If so, I’d be interested in recommended further reading.
To chime in as a person with grad-level training in the subject matter: there is a glaring tension between Quantum Field Theory and General Relativity in the low-energy macroscopic-size limit, which is very bad. How bad? Imagine “proving” that 1=2 in Peano arithmetic, something like that. The issue is the black hole: firewall or horizon? question. GR says that there is nothing locally special about crossing the event horizon (and must be applicable, since GR has been tested in this low-curvature regime), while QFT says that, after a while, the horizon becomes a high-energy incinerator (and must be applicable, since quantum entanglement has been tested in this low-energy regime). The best physics minds on the planet are at a loss to explain the problem. Last time something like that happened in physics, a completely new and unexpected theory eventually resulted. Odds are, we are in for a similar paradigm shift some day, hopefully soon.
Nobody’s resolved the fundamental problems between QM and general relativity (GR). EY comes close to claiming that MWI will do the trick, but it hasn’t yet. At one point he even says that (paraphrasing) reality is a dream, and the dream satisfies special relativity—at which point one has to ask why the dream doesn’t satisfy general relativity.
See the previous note. Emergence is just another word for “magic.”
This is an unfortunate side-effect of EY’s tone in the QM sequence.
The most evident problem in accepting both QM and SR simultaneously is that they substantially disagree on the value of the vacuum energy density.
What I think you’re saying, correct me if I’m wrong, is that there’s a few big unknowns as to how QM applies to gravity or on cosmological scales, and because of this the answer to my chain of reasoning is “we just don’t know”? That there’s major unknowns is entirely reasonable/accurate, but.. I’m struggling to see exactly how the very real and important unknowns apply specifically to my reasoning.
Simply put: Where, in the line of reasoning, do you think the unknown of quantum gravity trips up the logic, and why?
It’s seems quite possible that in discovering the answers behind the big unknowns we’ll change some underlying assumptions and render my reasoning unworkable. But I don’t see where in the line of reasoning not knowing vacuum energy density, or quantum gravity, causes a problem. And given that, it seems like working with the best available theory means applying certain aspects of QM at universal scale is not unreasonable, though we should expect we may need to update models once some big unknowns are resolved.
I think my use of emergence does not fall into the emergence/magic trap, since I am not attempting to explain anything about how large scale systems behave through emergence, my statement is purely that whatever the details of how macro systems work the large scale effects are caused by local physics being consistently applied and only appearing to work differently due to taking a larger view. Even though I used the word “emergence”, my sentence can be reworded with my intended meaning if you swap it to “emerges from”, which is specifically allowed by that post.
Also, you think my picture of reality as locally computable is “an unfortunate side-effect of EY’s tone in the QM sequence”? If that’s the case, do you dispute reality as locally computable? I’d be interested in sources which coherently argue for reality being non-locally computable.
We do know—QM predicts the wrong vacuum energy density by several orders of magnitude. We’ve measured this value empirically. Read the Baez link; he explains everything pretty clearly.
The critical unanswered question is how “underlying quantum effects” generate the (observed) geometry of space-time. If there were a solution to that question, I’d take no issue with you saying it emerges from those quantum effects—but we don’t know if it’s actually the other way around, that is, if it’s actually relativistic effects on the microscale that generate quantum phenomena. Or if this is just the wrong question entirely, and that both are caused by a third thing.
That’s how you fell into the emergence/magic trap.
EY has to spend a lot of time in the QM sequence insisting that QM is natural and fundamental to get over people’s preconceptions of it as unnatural. However, that leads to people taking it as the unique baseline physical theory, which it is not.
Okay, I think I see where you’re coming from better now. I have read that link, and at least feel like I conceptually understand some of the problems with applying quantum physics to the large scale. However, I’m still very curious as to exactly how the incompatibility in theories applies to this specific argument, and curious as to whether looking at a purely quantum universe (making the assumption that there is some way to derive relativistic experimental results from QM that we’ve missed, rather than that QM needs major changes) would give the results I’m describing, or whether I’m misunderstanding something about amplitude or thermodynamics in a heat death.
Hm, how to explain clearly.. It seems like what’s being said is QM is at odds with observation (vacuum energy density) and at odds with our other best theory, relativity, (event horizon, thanks for chiming in shminux), so QM is wrong or incomplete in some way. I accept this as a likely conclusion, though I do not understand either theory deeply enough to be able to follow the arguments for inconsistency in full.
However, dismissing a thought experiment about a widely used theory with some possible implications (if I’ve not missed anything and have understood various things better than I’d guess I have, that chain of reasoning could show a certain interpretation (MW) is incompatible with finite space+infinite time, while a different interpretation (collapse) would not be), due to the underlying theory (QM) being wrong/incomplete for other reasons seems.. limiting. Even if the line of reasoning only holds meaning with the assumption that the universe is fundamentally quantum, local, and macro effects are all explainable in principle by the laws which govern the smallest parts, I’m interested in whether or not it holds.
I’m primarily trying to refine my mental model of how decoherence works with these thoughts, and an answer focused on whether in a quantum universe would, from our current understanding of quantum physics, do as I suppose (that is, in finite space+infinite time, it could never even slightly decohere due to probability 1 arriving at an identical configuration eventually), or have I made some error in my reasoning which can be explained and would allow me to improve my model of decoherence?